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12 Volt battery Issues - Varied, Urgent

PRLM3

Member
Feb 16, 2019
103
28
Florida
Surprised at how little info on 12V battery there is out there - so sharing my recent experience. Just another day until went out to the M3 (12/18 delivery) and heard loud noise from frunk, didn't think much about as have heard similar when charging, but on entry to the car the windows barely moved down and behaved as if "battery" dying. Then got a steady procession of error messages about this not working that not working, etc. Real nightmare. Thought WTF, and just exited, let it sleep, then came back in. At that point all I had was the replace 12V battery soon message. Eureka I thought, no big deal. Seemed to behave fine, then on driving I noticed the fan for the AC would not blow. In October in Miami that's a big deal.

Went through the service app and got an appointment for like 6 weeks out. No es bueno. Beat my head against voice mail jail prompts trying to get to my local service center. While I was on extended hold, Tesla service via the app had rescheduled me for only 5 days out which I thought was great, but still longer than I wanted with no AC. Hoping to fenagle my way into a "quick 12 volt swap" at the dealer I hung in there, and eventually got a service person who told me he wasn't sure if the fan was related to the 12 volt issue or not, but "don't worry about it because when you see the light you still have a long time before the battery actually goes."

The next day, my AC fan began blowing again. Meanwhile, I was doing a lot googling and found videos on how to swap the 12V out but not really anything on symptoms. Over the next 4 days, I had major failures to include headlights and brakes, and little stuff like the windows not aligning correctly. Favorites were on way home from work pulling down my streets and "click" the headlights went out. Poof! Running lights stayed on, but no fun. Next night in parking garage at work put foot on brake to wake car and immediately felt stiff resistance and brakes basically required huge amount of pressure to get to a full stop - thank God for regen braking.

At this point I didn't know if I was just having a series of catastrophic computer issues or if the 12V was crazy important focal point of the vehicle, and the service guy was (forgive me) a complete idiot. The mobile guy showed (raining!) and quickly assured me that everything I had been experiencing was not unusual, and that when you see a 12V light you should get the battery replaced right away, and that the mobile service prioritizes those calls to the "top" of their list. He actually asked me if I got a name from the service center because he was ready to "call and ream him a new one" - I appreciated the passion and attention to customer safety. BTW, he said 18-24 months is the average life span and added "so you're right on schedule." He also added that every time you wake the car even if you don't even get in it, you're cycling the 12Volt which is why they go so quick. (BTW, mine was $0 under warranty.)

In summary, when you get a 12V warning:
  • Get it fixed as fast as you possibly can
  • Know that really any symptom may pop up spontaneously to include really serious safety issues
  • Window issues are the most common (if you have one, make sure they re-calibrate when swapping battery)
  • Per mobile tech, all this is pretty much the same for the S, the X and the 3.
 

KenC

Active Member
Sep 4, 2018
3,602
3,271
Maine
He also added that every time you wake the car even if you don't even get in it, you're cycling the 12Volt which is why they go so quick.

Interesting. So, using a 3rd-party app like Stats which seems to wake the car constantly, would kill your battery faster. My car is coming up on its 2nd birthday, and I've had Stats for almost that whole time. I guess I should be prepared for it to start going wonky.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
9,488
10,664
Riverside Co. CA
Interesting. So, using a 3rd-party app like Stats which seems to wake the car constantly, would kill your battery faster. My car is coming up on its 2nd birthday, and I've had Stats for almost that whole time. I guess I should be prepared for it to start going wonky.

@AlanSubie4Life had some interesting (to me) info about 3rd party apps, from his experience monitoring his car. The TL ; DR if I remember it was that "even if the apps say they dont wake the car, or change sleep patterns, they do".

Not trying to put words in his mouth though so tagging him here in hopes he could either link to his other post on it, or summarize.


My car is coming up on 2 years old (dec 2018) with 27k miles, and a showing max range of about 294 miles. its been very good to me so far, and I dont use any third party monitoring at all. I am hesitant to replace the 12v on my own dime, since it will be covered under warranty for a while yet, but I also dont want to get stranded somewhere.
 
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AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
9,989
12,034
San Diego
Interesting. So, using a 3rd-party app like Stats which seems to wake the car constantly, would kill your battery faster.

You can look up some of the 12V battery monitor plots I have posted.

I have disabled Stats since he seems to have screwed up the programming, so it is constantly hammering the contactors and waking up the car every hour (easy to see with the monitor).

I’m not convinced that cycling the 12V regularly is really an issue - it will go to a maintain voltage if the battery does not need charging. I worry more about 10x as many cycles on the contactors, in spite of what they are rated for.

I am hesitant to replace the 12v on my own dime, since it will be covered under warranty for a while yet, but I also dont want to get stranded somewhere.

Battery is $85 FWIW. No core charge from what I understand. Can be replaced yourself. No special procedure needed.

As far as sleep patterns go, I can only tell you what Stats does. I don’t think it was always this way. My understanding is that it is possible to design a third-party app so as to not wake up the car all the time, but that is not what is currently done with Stats.

Anyway the 12V monitor makes it easy to figure out what is happening.
 
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KenC

Active Member
Sep 4, 2018
3,602
3,271
Maine
@AlanSubie4Life had some interesting (to me) info about 3rd party apps, from his experience monitoring his car. The TL ; DR if I remember it was that "even if the apps say they dont wake the car, or change sleep patterns, they do".

Not trying to put words in his mouth though so tagging him here in hopes he could either link to his other post on it, or summarize.


My car is coming up on 2 years old (dec 2018) with 27k miles, and a showing max range of about 294 miles. its been very good to me so far, and I dont use any third party monitoring at all. I am hesitant to replace the 12v on my own dime, since it will be covered under warranty for a while yet, but I also dont want to get stranded somewhere.
I understand the battery is warranted, but my time wasted waiting for a tow truck to take me to a SC, is worth far more to me than the $85 cost of a backup battery. I know it's letting Tesla off the hook, but the SC is 2+ hrs from me!
 

PRLM3

Member
Feb 16, 2019
103
28
Florida
I understand the battery is warranted, but my time wasted waiting for a tow truck to take me to a SC, is worth far more to me than the $85 cost of a backup battery. I know it's letting Tesla off the hook, but the SC is 2+ hrs from me!
Yeah if you're 12/18 I'd pick one up and have it around just in case. I know there have been reports about sudden outage with no warning, but like I said I had plenty of warning. I did get the HW3 upgrade and obviously the updates; I'm not sure if that had anything to do with the warning. Do check out the YT vids on it though, you need to disconnect the high voltage systems which are under the back seat, so it's not quite like just swapping out the battery on a motorcycle or generator.
 
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towndrunk

Member
Jun 2, 2018
290
205
Fargo, ND
I'm 4 hours from the nearest SC and took delivery on 9/18. At least I'm in ND, not TX or FL where the high temps are harder on the battery.

I found a good deal on a battery tester on eBay so that will be my insurance for now.
 

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